Nitriles such as acrylonitrile and methacrylonitrile have long been industrially produced as important intermediates for the preparation of synthetic fibers, synthetic resins, synthetic rubbers and the like. A major use of acrylonitrile is in the form of fibers. Acrylonitrile-butadiene-styrene terpolymers (ABS) are important thermoplastic structural plastics. Nitrile-type rubbers, first commercialized as the German Buna-N type in 1930, are copolymers of acrylonitrile and a diene, usually butadiene.
The currently practiced commercial processes for the production of nitrites, such as acrylonitrile and methacrylonitrile, subject an alkene, i.e., propylene or isobutene, to reaction in a gas phase with ammonia and oxygen in the presence of a catalyst at a high temperature. Generally, the catalyst formulations employed are proprietary to the catalyst supplier, but the technology is well established. Furthermore, it is known to include additional starting materials, including additional reactants, such as molecular oxygen and/or steam, and inert materials, such as nitrogen and carbon dioxide, along with the hydrocarbon starting material.
Recently, in view of the relative abundance of lower alkanes relative to corresponding alkenes, resulting in price differences particularly between propane and propylene or between isobutane and isobutene, attention has been drawn to developing improved catalysts for producing nitrites from these, less expensive, lower alkanes. Propane or isobutane is used as starting material in a so-called ammoxidation reaction with ammonia and oxygen in a gas phase in the presence of a catalyst.
Catalysts containing molybdenum, vanadium, antimony and niobium which have been shown to be effective for conversion of propane to acrylonitrile and isobutane to methacrylonitrile (via an ammoxidation reaction) are described in numerous publications, patents and patent applications. See, for example, U.S. Pat. No. 5,750,760 to Ushikubo et al., U.S. Pat. No. 6,036,880 to Komada et al., U.S. Pat. No. 6,143,916 to Hinago et al., U.S. Pat. No. 6,514,902 to Inoue et al., U.S. Patent Application No. US 2003/0088118 A1 by Komadu et al., U.S. Patent Application No. 2004/0063990 A1 to Gaffney et al., U.S. Patent Application No. 2006/0167299 A1 to Gaffney et al., U.S. Patent Application No. 2006/0122055 A1 to Gaffney et al., U.S. Patent Application No. 2006/0183942 A1 to Gaffney et al., PCT Patent Application No. WO 2004/108278 A1 by Asahi Kasei Kabushiki Kaisha, Japanese Patent Application No. JP 1999/114426 A by Asahi Chemical Co., and Japanese Patent Application No. JP 2000/1126599 A by Asahi Chemical Co.
Oxide catalysts containing molybdenum, tellurium, vanadium and niobium are described in U.S. Pat. No. 5,049,692, U.S. Pat. No. 5,231,214, U.S. Pat. No. 5,281,745, U.S. Pat. No. 5,380,933, and U.S. Pat. No. 5,422,328. Further, oxide catalysts containing molybdenum, vanadium, niobium and antimony are described, for example, U.S. Pat. No. 4,760,159, U.S. Pat. No. 4,797,381, U.S. Pat. Appl. No. 2005/0054869 to Lugmair et al. and U.S. Pat. Appl. No. 2006/0122055 to Gaffney et al. However, none of these methods is fully satisfactory in the yield of the intended nitrites.
Although advancements have been made in the art in connection with catalysts containing molybdenum, vanadium, antimony and niobium effective for conversion of propane to acrylonitrile and isobutane to methacrylonitrile (via an ammoxidation reaction), the catalysts need further improvement before becoming commercially viable. In general, the art-known catalytic systems for such reactions suffer from generally low yields of the desired product.
Due to their extensive industrial uses, there is a continuing need for compositions having better catalytic activity and/or selectivity for ammoxidation of lower alkane hydrocarbons to produce an unsaturated nitrile in high yield
It is an object of the invention to overcome one or more of the problems described above.
Other advantages of the invention will be apparent to those skilled in the art from a review of the following detailed description, taken in conjunction with the appended claims.